1. Field of the Invention
The present invention generally relates to an image formation apparatus and a sublimation printer. More specifically, the present invention relates to an image formation apparatus and a sublimation printer which transfer ink from an ink ribbon onto paper by electrical heating of a thermal head.
2. Background Information
With a conventional sublimation printer, a platen roller is rotatably attached between side panels of a main frame, and a thermal head is disposed across from this platen roller. This thermal head is supported on a head assembly, which is pivotably attached to a plate provided on the inside of the side panels of the main frame. The pivoting of the head assembly causes the thermal head to move away from the platen roller. The printer is provided with a torsion spring for generating a biasing force that causes the head assembly to pivot so that the thermal head moves away from the platen roller, and a coil spring for generating a biasing force that presses the head assembly against one of the side panels of the main frame. The torsion spring is designed to keep the thermal head away from the platen roller when not printing, and the coil spring is designed to prevent the thermal head from becoming misaligned in the axial direction of the platen roller. Also provided are a press lever of which the pivoting causes the head assembly to pivot, thereby pressing the thermal head against the platen roller, and a drive component for pivoting this press lever.
With a sublimation printer, the printing of text or graphics is accomplished by laying an ink ribbon and paper one over the other, passing them between the thermal head and the platen roller, and applying heat to the thermal head during this passage so that the ink in the ink ribbon will be transferred to the paper. If there is any misalignment of the thermal head in the axial direction of the platen roller during this process, the printing of the text or graphics on the paper will also be misaligned. The above-mentioned coil spring is provided so that this will not happen.
Also, the above-mentioned torsion spring is provided in order to prevent the thermal head from pressing on the platen roller when no printing is in progress, such that deformation of the platen roller and shortening the service life of the thermal head can be prevented.
It has been proposed in Japanese Patent Application Publication 9-71022 to attach a spring diagonally between a head press bar and a thermal head, so that the biasing force of this spring will prevent the misalignment of the thermal head in the axial direction of the platen roller during printing. Also, the thermal head will press on the platen roller with uniform pressure. This head press bar corresponds to the portion that supports the thermal head in the above-mentioned head assembly.
However, with a conventional sublimation printer, as discussed above, the torsion spring for keeping the thermal head away from the platen roller while the printing is not in progress, and the coil spring for preventing the misalignment of the thermal head in the axial direction of the platen roller are separately required. Thus, such conventional sublimation printer requires many parts, which is a problem in that the component cost is higher. Also, because of the greater number of parts, its assembly entails more labor. As a result, assembly costs incurred in the assembly of such conventional sublimation printer also end up being high.
Japanese Patent Application Publication 9-71022 proposes to generate a biasing force for preventing the misalignment of the thermal head in the axial direction of the platen roller, and a biasing force for maintaining uniform pressure of the thermal head on the platen roller, with a single spring. However, Japanese Patent Application Publication 9-71022 does not disclose or suggest a single elastic member that generates biasing force for keeping the thermal head away from the platen roller as well as the biasing force for preventing the misalignment of the thermal head in the axial direction of the platen roller.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image formation apparatus and a sublimation printer that overcome the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.